Regulation of car chargers. Is your car charger killing your expensive iPhone

[haxby]

There are many car chargers on the market that use a standard 5V USB plug. Some are rated at 500ma and others 1A.

There is one available at Jaycar at the moment that claims a 1.2A output. I recently purchased 3 different USB car cigarette lighter adaptors, and I measured the ripple voltage at various loads. The results were quite surprising. None of them had a ripple voltage of less than 100mV at 500mA, and at full load the ripple voltage was nothing short of attrocious. They probably only work because the phones themselves have filter caps installed to combat this.

These devices have become smaller and smaller, and the current batch sit flush with the cigarette lighter. So there is not much room for any filter caps or inductors. I wonder if Dave could use his universal dummy load that he has just built to do a few tests of common cigarette to USB adaptors.

This would be a cheap tutorial as the parts would cost less than $20, and some quick CRO shots woud be very beneficial for many users of these devices.

[Pyr0Beast]

There definitely IS place for capacitors. But they cost money
Open one up. There must be a MC34063a inside

[Simon]

There definitely IS place for capacitors. But they cost money
Open one up. There must be a MC34063a inside

now what the hell you thinking spending money on capacitors, cmon don't be silly thats 2 pence you can save 

[squeezee]

Yeah all the car chargers i've opened use an 34063 and also tend to resemble the datasheets step-down schematic, which specifys a ripple of ~120mVpp@500ma (with 24V in). So i wouldn't say that what you're seeing is unexpected.

They could add extra filtering to cut ripple, it's even in the datasheet, but i haven't seen it done.

[sigxcpu]

As far as i know iPod Touch works with 5-30VDC for charging/usage, so i assume that iPhone does that, too.
The cheap car adapter will kill other devices maybe, but iPhone is out of the list

[Markjupiter]

Having a car adapter for iPhone is really helpful in case of emergency. So I am interested in having this car adapter even if it is expensive. Where do we usually find this stuff?

[sigxcpu]

I think every store on earth with phone accessories have them.